It was 1988 and the then-vice president, George H. W. Bush, was on a routine visit to Idaho. He was supposed to give a dry speech on agricultural policy and praise his successes alongside President Reagan, live on television. Then he said: “We’ve had triumphs. Made some mistakes. We’ve had some sex... uh... setbacks.”

Long after his political career is consigned to distant memory, President George Bush Senior will be celebrated for this legendary gaffe.

Ah, the Freudian slip. There are the things you want to say, the things you could get away with saying and the things it would be utterly disastrous to utter – which, invariably, are what actually comes out of your mouth. It’s the greatest fear of any public speaker. But what really causes these errors? And do they have any hidden meaning?

For Sigmund Freud, the founder of psychoanalysis, it wasn’t enough to simply ask his patients what they thought. Their true desires, he believed, could only be examined by paying attention to ‘slips of the tongue’ and other clues from the unconscious. A classic slip is, as the saying goes, when you say one thing and mean your mother.

Otherwise known as parapraxis, these verbal stumblings could reveal forbidden urges – such as sex and swearing – which were usually locked safely within the unconscious mind. Verbal errors aren’t random at all, but puzzles to be decoded.

There’s just one problem: Freudian slips, as with many of his other ideas, are extremely difficult to test. Freud may be as famous as Darwin, but many modern-day psychologists, linguists and neuroscientists think that he was wrong about almost everything. But was he wrong about this?

One ingenious early study used sex and electric shocks to find out. At the start of the experiment, two of three groups of heterosexual males were greeted by a middle-aged professor, while the third was ushered into a room with a provocatively dressed lab assistant. “We sort of went to the limits of what one might expect on campus. She was attractive and wearing a very short skirt and sort of a translucent blouse,” says Michael Motley, a psychologist from the University of California Davis who co-authored the study.

Participants were asked to read a list of word pairs (‘back mud’, ‘bat much’, ‘mad bug’) silently, at a rate of one per second. What they didn’t know was that the word pairs had been designed to induce ‘spoonerisms’, slip-ups named after the error-prone Reverend William Archibald Spooner, in which the initial sounds or letters in two words are switched.

Every so often the experimenters indicated, via a buzzer, for subjects to say a pair out loud. As Freud would have predicted, the men in the presence of the lab assistant made significantly more sex-based slip-ups (‘fast passion’ instead of ‘past fashion’ and ‘happy sex’ instead of ‘sappy hex’) than the control group, but no more slips overall.

Meanwhile the third group had their fingers hooked up to electrodes, plugged into a machine capable of delivering mild electric shocks. “We told the fellows – this was a lie, of course – there’s a 70% chance you’re going to get a shock,” says Motley. Again, the students let slip what was really on their mind (misreading ‘worst cottage’ as ‘cursed wattage’ and ‘shad bock’ as ‘bad shock’).

Later the experimenters measured the participants’ sexual anxiety and discovered, counter-intuitively, that those with the most carnal angst made the most sexual missteps. Why?

In attempting to suppress their urges, the men may have fallen victim to the ‘white bear problem’, first noticed by Russian author Fyodor Dostoyevsky. Try hard enough not to think of something, such as sex or a polar bear, and it will be all you can think about. It’s the basis for The Game, a popular mind game which challenges players to avoid thinking about its existence. Let it sneak into your conscious and you lose, and must announce your loss out loud – causing everyone around you to lose also. To win… well no one’s figured that one out yet.

Back in the 1980s, psychologist Daniel Wegner suggested that the very system which aims to prevent Freudian slips may be to blame. According to his theory, subconscious processes are continuously scouring our thoughts to keep our innermost desires locked away. When such a thought occurs, instead of remaining quiet – ironically – the thought may be announced to the conscious brain, causing you to think it.

Then it’s only a matter of time before the truth slips out. “When we’re thinking about something we’re priming the relevant words, they’re being prepared to be spoken in case we need them,” says Motley. With so many options, the word we end up choosing can be revealing.

Take the sentence “The old hillbilly kept his moonshine in a big (blank)”. In another version of the sexual arousal experiment, Motley asked participants to choose the last word. Lots of words – pitcher, barrel, jar – are viable candidates, but more often than not those who felt attracted to his lab assistant chose ‘jugs’. “It’s sort of doubly primed and it gets selected over the others. We think something similar is happening with Freudian slips,” says Motley.

Deliberately try not to tell your gym partner “you’re very fat – I mean fit!”, blurt out “pornography” at a meeting rather than “photography” or call out your ex’s name during sex, and you’ll be inviting subconscious sabotage. To add insult to injury, being stressed makes these catastrophic blunders even more likely.

But not everyone is convinced. At the time, Freud’s harshest critic was Austrian linguist Rudolf Meringer. While working at the University of Vienna in the late 19th Century, Meringer collected, catalogued and scrutinised thousands of verbal mistakes, mostly from lunchtime conversations with colleagues. The group would take turns speaking and when an error occurred, they would cease all conversation until it had been meticulously recorded.

From this record, Meringer concluded that slips of the tongue are intrusions of letters, not meaning. In fact, according to Rob Hartsuiker, a psycholinguist from Ghent University, the majority of errors are entirely innocent.

Take the unfortunate blunder by journalist Jim Naughtie, who slipped up while pronouncing the then-Culture Secretary Jeremy Hunt’s surname on BBC Radio 4’s Today programme. At first glance it looks like a classic Freudian mishap; in fact, it reveals more about how the brain processes language than Naughtie’s feelings about the politician.

A mountain of experimental evidence has shown that if two words share contextual meaning and a vowel, the initial consonants are at risk of getting mixed up. “I’m sure many people don’t find Jeremy Hunt a very pleasant person, but it’s actually an intrusion of the ‘c’ from culture,” says Hartsuiker.

It’s the result of the way words are accessed in the brain. First, one must be selected from a network of words which are organised by similarity and meaning – an opportunity to mix up Culture and Hunt. Once you have the word, the brain selects the word sounds – which is when the consonants are swapped. “This is very typical, and it’s also something Freud rather ignored,” says Hartsuiker. As the program’s co-host pointed out at the time, you might say appointing a man with the name Hunt as the Culture Secretary was extremely reckless.

Despite these verbal traps, the average person slips up on fewer than 22 words per day out of around 15,000. Brain scans have shown that we routinely make embarrassing blunders while rehearsing our sentences in ‘inner speech’, but the majority are caught before we say them out loud. “What is produced at the end is correct but brainwaves reveal that internally they made the taboo mistake,” says Hartsuiker, who co-authored the study.

We’re probably more vulnerable to slips when we’re distracted or our unconscious spellchecker isn’t working properly – if we’re nervous, tired, or intoxicated and as we get older. You’re also more likely to trip up if you’re talking too quickly.

In other words, our verbal slips may reveal something interesting about the way the brain processes language, and they may even suggest our current preoccupations we’d rather not discuss. But whether they ever tell our deepest secrets is still a matter of debate. Psychoanalysts like Rosine Perelberg from University College London certainly think they are important. “They are very much the stuff of jokes, but they are so precious because they betray something the person did not want to consciously reveal,” she says. “We take them very seriously.” She mentions a recent patient whose slip revealed subconscious anxieties about being violent towards his future child (he said battle instead of bottle).

Hartsuiker is sceptical. “The evidence for real Freudian slips is very, very limited indeed.” For others, it’s likely that the explanation depends on the slip. “Do I agree with Freud that all slips are Freudian? Well, no. But do I think that there is such a thing? Yes I think so,” says Motley.

So which kind was President George W. Bush’s slip-up? We’ll never know for sure, but they were probably just partners in copulation… sorry… collaboration.

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